1. Field of the Invention
The present invention is related to prior art found in the fields of antistatic fibers, coating processes, and electroless deposition of metals onto substrates. More specifically, the present invention pertains to a conductive fiber and process for making, the process broadly comprising: (a) catalyzing a polymeric material, followed by (b) electrolessly depositing a metal within the polymeric material.
2. Description of the Prior Art
Prior to the reduction to practice of the present invention, the electroless deposition of metals on polymeric materials resulted in a coating of metal upon the polymeric material, as opposed to metal deposition coincident (i.e. within, impregnated into) the polymeric material. Most prior art processes of making electrolessly plated polymeric filaments involved first roughening the surface of the filament (using abrasive materials or acids) followed by catalysis of the surface, followed by electroless deposition of metals at catalytic sites which in turn was followed by autocatalytic deposition of even more metal. Since the prior art processes never formed catalytic sites within the polymer structure, but rather formed catalytic sites only on the surface of the polymer, the resulting deposition of metal formed only a metallic coating on the surface of the polymer. The prior art catalysts were unable to penetrate the polymer structure in order to form catalytic sites within the filamentary polymeric substrate. Furthermore, the antocatalytic activity of the metal being deposited never resulted in the "inward" deposition of metal (i.e. deposition of metal in a direction towards the center of the filamentary cross section). Rather, the autocatalytic activity of the deposited metal resulted in a thicker and thicker coating of the deposited metal onto the surface of the filamentary polymeric substrate. Thus the resulting conductive filament was comprised of two distinct regions: (a) an inner nonconductive polymeric core surrounded by (b) a conductive outer metallic layer. One of the most bothersome characteristics of these conductive filaments was that the adherence of the metal coating to the polymeric substrate was poor, and as a result the metal coating would often chip or pull off in subsequent filament handling or processing operations. For this reason, electrically conductive filaments produced via electroless deposition of metals have not generally been commercially successful.
Applicant is aware of several prior art patents which are relatively close to, but different from, the present invention, including: U.S. Pat. Nos. 4,201,825; 3,686,019; 3,823,035.
U.S. Pat. No. 4,201,825 discloses a process for manufacturing conductive filaments via electroless deposition of metals, but in this patent the metals are deposited only on the surface of the filaments:
"Accordingly, the invention relates to a metalized (metal-coated) textile material, for example filaments, fibers and textile structures, which is obtainable for . . . " Column 1, lines 39-41.
"The residence time of the material to be metalized in the described metalizing bath is determined by the required thickness of the metal layer on the surface of the material." Column 2, lines 13-16.
After only thirty seconds, the fabric is covered with a thin layer of nickel and is dark in color. After about five minutes, the nickel layer has a thickness of 0.2 micrometers. Column 4, lines 5-7.
U.S. Pat. No. 3,686,019 also discloses only the deposition of metals on the surface of the filaments:
"According to our further developments of the above prior improvement, it is surprisingly found that a highly effective metal coating is realized on a chemical fiber, preferably a thermoplastic fiber, when it is sensitized and activated by deposition on its surface of a nobel metal catalyst . . . " Column 2, lines 31-35.
Thickness of the metal coating layer should be 0.01 micron, preferably, 0.025-0.25 micron. "Column 5, lines 53-54"
"A representative process . . . the thus treated fibrous material is immersed in a catalyzer solution containing nobel metal ions, so as to separate the metal onto the fiber surface . . . " Column 6, lines 11-16.
U.S. Pat. No. 3,823,035, a prior art patent issued to the inventor of the instant invention, also teaches a product and process pertaining to conductive filaments. However, this product has: ". . . finely-divided, electrically-conductive particles uniformly suffused as a phase independent of the polymer substrate . . . " Column 2, lines 41-43.
These conductive particles which are suffused into the polymer are each distinct from one another, and it is known that the conductive characteristics of these filaments result from the fact that the particles are in close enough proximity to one another that an electrical charge will "jump" from particle to particle in its flow through the filament. At least a portion of the conductive particles described in U.S. Pat. No. 3,823,035 are definitely within the polymeric material itself, as opposed to a coating on top of the surface of polymeric material. However, it is believed that these conductive particles do not form an "electrically continuous zone" (i.e. a region through which electrons may flow along a continuous path without having to "jump" from one conductive member to another).